Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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  #21   Report Post  
Old January 13th 20, 08:05 PM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

On Mon, 13 Jan 2020 12:09:44 +0000, Cursitor Doom
wrote:
I'm afraid I don't have that option at the moment. The 2465A blew up a
couple of days ago and has now joined my pile of "awaiting attention"
junk. I didn't blow it up, by the way; it managed it all by itself.


See my comments on divine retribution elsewhere in this thread.

I think you may have missed the clarification I posted.


Yep. I read your comments after I posted my comments. I often read
Usenet threads starting from the most recent, rather than in
chronological order. That saves me the embarrassment of answering
questions that were previously answered, but also causes me to miss
important added information.

My working practices are a bit slapdash
I must admit, but no worse than the average hobbyist I would imagine.


Yep.

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

  #22   Report Post  
Old January 13th 20, 10:40 PM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

Jeff Liebermann wrote in
:

Divine retribution and intervention are quite different. Divine
retribution is where a lightning bolt from out of the clear blue sky
strikes the transgressor down following a chronic failure to RTFM and
follow the instructions.


https://en.wikipedia.org/wiki/Roy_Sullivan

https://funfactz.com/amazing-facts/walter-summerford-lightning/
  #23   Report Post  
Old January 14th 20, 06:42 PM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

I've now uploaded 3 photos of what I'm seeing. The most obvious noise
(apart from being obvious) is the 'comb' across the screen. I'm
getting the most spurii at the lowest 'fundamental' (around 5Mhz) but
as I sweep up in frequency the number of spurs declines markedly so by
200Mhz there are only 4 spurs remaining and they're much wider apart.

The other form of noise I mentioned in an earlier post is the more
attenuated and spread out one visible just to the right of the
centre-frequency line. This noise, unlike the 'comb' is constantly
flickering and random.



https://yandex.com/collections/card/...e97d27c81ef46/
--

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Old January 14th 20, 09:28 PM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

On Sun, 12 Jan 2020 20:21:53 -0800, Jeff Liebermann
wrote:

Yep. Failure to observe my advice will result in divine retribution.


Not to mention ingominous failure!
Well, the traces I'm seeing (and have now posted images of to the
group) do bear a certain distinct similarity to what you described,
Jeff, so if that be the case I'm wondering if one of the oscillators
is being over-driven. I'm guessing that might give rise to 3rd
harmonic spurii, don't you think?

--

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Old January 16th 20, 06:05 AM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

On Tue, 14 Jan 2020 17:42:04 +0000, Cursitor Doom
wrote:

I've now uploaded 3 photos of what I'm seeing. The most obvious noise
(apart from being obvious) is the 'comb' across the screen. I'm
getting the most spurii at the lowest 'fundamental' (around 5Mhz) but
as I sweep up in frequency the number of spurs declines markedly so by
200Mhz there are only 4 spurs remaining and they're much wider apart.

The other form of noise I mentioned in an earlier post is the more
attenuated and spread out one visible just to the right of the
centre-frequency line. This noise, unlike the 'comb' is constantly
flickering and random.

https://yandex.com/collections/card/...e97d27c81ef46/


Sorry for the late reply, but I had to waste the last few days dealing
with the California Dept of Motor Vehicles to renew my drivers license
and obtain a Real-ID endorsement. I passed both but am still
recovering and might need a few more days to calm down.

Interesting spectrum analyzer display and description. The most
interesting part is how you managed to produce the photo, without
bothering to mention the:
1. Network analyzer test Frequency
2. SA (spectrum analyzer) horizontal MHz/div.
3. SA vertical full scale, dBm per division, and dBm full scale.
4. Whether you were misusing a scope probe (again) or feeding it
with 50 ohms. Also, any attenuators or couplers in the RF path.
5. Did you remember to turn of the 1, 10, 50Mhz markers on the
HP8754A?
6. Any other numbers which might be useful, especially those you
previously mention, but which I'm too lazy to dig through your old
postings to find.

Had you supplied some numbers, I would have dived into the HP8754A
network analyzer service manual, and determined the frequencies of the
two oscillators (3.6 - 4.3GHz minus 3.6 - 3.0GHz) used to produce your
unspecified output frequency. I would then compare the possible
intermodulation mixes of these two frequencies, with the mess on your
spectrum analyzer screen, and see if any of the spurs are the result
of oscillator feedthrough, intermod mixing, or overdriving the
spectrum analyzer and creating the spurs in the SA. However, since
your photos were not accompanied by any numbers, I can't do this for
you. Incidentally, you might want to ask in one of the HP test
equipment forums for what a working HP8754A RF output looks like on a
spectrum analyzer. I would not be surprised if the mess on your
screen is quite normal.

Incidentally, if you download and read the HP8754A service manual,
you'll find a large number of Performance Tests. Performed properly
in the manner specified, you should get a better idea if your network
analyzer is functioning as expected.

Also, this is your second warning about providing insufficient
information and numbers. Provide numbers with your problems or
prepare thyself for the wrath of the radio gods. The recent failure
of your Tek 2645A scope was a poorly aimed warning shot (I was aiming
for your Tek 2232A scope) and a hint of things to come.


--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


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Old January 16th 20, 11:14 AM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

On Wed, 15 Jan 2020 21:05:43 -0800, Jeff Liebermann
wrote:

Sorry for the late reply, but I had to waste the last few days dealing
with the California Dept of Motor Vehicles to renew my drivers license
and obtain a Real-ID endorsement. I passed both but am still
recovering and might need a few more days to calm down.


My sympathies. I've heard about the queues in those places and they
must be pretty bad indeed to make the international news! Is it true
they recruit retired-disabled ex-NYC taxi drivers for their counter
staff?

[snip missing numbers]

Yeah, I know. I'm sorry but you know about as much as I do! If I'd
zoomed out on those shots there's a bezel around the outside of the
screen on that SA which is *supposed* to show all that info.
Unfortunately, it's bust. This is a partly working unit I picked up at
a ham rally and am in the process of re-commissioning. Unfortunately,
my No.1 RF SA (the 8566B) is currently out of action with a recent
"YIG oscillator unlocked" error message, so there's nothing to fall
back on. It's kind of tough to do stuff with all this busted
equipment. Even the equipment I picked up in prime working condition
is letting me down lately.
All I *can* say about those photos is the SA is set on the 0.01-1.8Ghz
display range, I'm sniffing the VNA output with a few turns of wire
rather than a direct connection, the 40dB attenuation is set (and
seems to work!) and the VNA output frequencies in each picture are the
filenames for each of those pictures.
So the situation is "not ideal" but you have to work with what you've
got, I guess.
--

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Old January 16th 20, 11:42 AM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

On Wed, 15 Jan 2020 21:05:43 -0800, Jeff Liebermann
wrote:


I just noticed some points you mentioned I forgot to cover in my
earlier post...

1. Network analyzer test Frequency


Shown in picture title for example 10Mhz.jpg means the VNA was set to
10Mhz.

2. SA (spectrum analyzer) horizontal MHz/div.


Full band mode so ~180Mhz/div.

3. SA vertical full scale, dBm per division, and dBm full scale.


No reliable info.

4. Whether you were misusing a scope probe (again) or feeding it
with 50 ohms.


Neither - sniffing with few turns of wire.

Also, any attenuators or couplers in the RF path.


Nope. Just the 40dB attenuation setting of the SA.

5. Did you remember to turn of the 1, 10, 50Mhz markers on the
HP8754A?


Yep, no markers.

Incidentally, you might want to ask in one of the HP test
equipment forums for what a working HP8754A RF output looks like on a
spectrum analyzer. I would not be surprised if the mess on your
screen is quite normal.


Good suggestion.

Incidentally, if you download and read the HP8754A service manual,
you'll find a large number of Performance Tests. Performed properly
in the manner specified, you should get a better idea if your network
analyzer is functioning as expected.


I do actually have the original physical hard-copy of the service
manual and was working my way through those performance tests when I
got side-tracked by something else whilst waiting for the required
phase-matched power splitter and some new terminations to arrive. I
really MUST get back to that as they have since turned up in the post.

I also need to try out some other poster's suggestion re sweeping the
VCO ramp with DC from batteries, too. So I have plenty to get on with
whilst you digest my replies, Jeff. :-/
--

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  #28   Report Post  
Old January 16th 20, 01:52 PM posted to sci.electronics.design,sci.electronics.repair
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Default Noise on VCO voltage ramp

The VNA was putting out 10dBm in all those photos, btw. I'm reasonably
confident that much at least is 'pretty accurate.'

--

No deal? No problem! :-D


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